1. Field of the Invention
The present invention relates to a projection display unit for displaying a projected image and to a method for controlling image display when displaying a projected image.
2. Description of the Related Art
A liquid crystal projector is widely known as a projection display unit for displaying projected images. The liquid crystal projector modulates light from a light source in a liquid crystal panel to create an optical image in accordance with image signals and displays an enlarged optical image on a screen via a projector lens. An iris diaphragm mechanism (hereinafter, simply referred to as an “iris diaphragm”) is provided between the liquid crystal panel and a projector lens. A transmission amount of light after being modulated in the liquid crystal panel is regulated in accordance with a diaphragm diameter of the iris diaphragm. In this manner, the luminance of the image projected on the screen may be changed.
The luminance of a projected image may be controlled through analysis of a histogram of a luminance signal distribution of image signals for an image to be projected. In particular, a frequency count is accumulated from either a high-luminance end or a low-luminance end of the created histogram. A class of the histogram where the accumulated frequency class exceeds a threshold is detected. A diaphragm diameter of the iris diaphragm is determined by using a value uniformly specified from the class. In particular, the diaphragm diameter of the iris diaphragm which may directly affect the luminance of the projected image is determined on the basis of a search result from either the high-luminance end or the low-luminance end of the histogram in order to control the luminance of the projected image (for example, see Japanese Unexamined Patent Application Publication No. 2002-268116).